The present invention relates to a thin stator suitable for use as silent call means for a portable communication device and the like, an eccentric rotor, and an axial air-gap brushless vibration motor equipped with the same.
Flat axial air-gap brushless vibration motors have been previously proposed, for example, in Laid-open Japanese Utility Model Application No. H4-137463 and Laid-open Japanese Patent Application No. 2002-143767, and include a motor of a coreless slotless type comprising a bearing.
Known brushless vibration motors, for example, as disclosed in Laid-open Japanese Patent Application No. 2000-245103, are equipped with a drive circuit, and include a noncircular motor of a cored type comprising a plurality of equidistantly disposed salient poles and an armature coil wound therearound, and a drive circuit member disposed in a stator.
However, a motor according to such design tends to be long in the lateral direction, decreasing mounting efficiency in the case of a printed wiring board in the SMD style. Further, because it is a cored type, such motor invariably becomes thick and thus serves no practical purpose.
Another proposed motor, disclosed for example in Laid-open Japanese Patent Application No. 2002-142427, includes both cored and slotless coreless types, wherein some of a plurality of armature coils are removed to create a dead space, and a drive circuit member is disposed in the dead space.
A single phase motor driven by a single Hall sensor requires a magnetic detent torque generation member for making the rotor magnet stop at a specific position so as to ensure the subsequent start.
In order to obtain the desired detent torque generation force, the detent torque generation member requires a certain thickness, with a detent torque generation member disposed on a bracket. Consequently, it is difficult to find space for disposition, and the configuration operates against the goal of forming a thinner motor.
Further, when the detent torque generation member is formed by printing, for example, to obtain the desired detent torque generation force, the detent torque generation member again needs to have a certain thickness and width. But increasing width makes the position of a detent torque generation member unstable, and decreasing width, on the other hand, will result in a substantial sacrifice of thickness.
Meanwhile, there is another proposed motor wherein detent torque parts of a detent torque generation member are accommodated within the inner diameter of an air-core armature coil so as to axially protrude therefrom, enabling the thickness of the detent torque generation member to be substantially ignored. However, such motor is problematic in that its coil inner diameter is limited, restricting the number of windings on a coil. More specifically, the disposition position of a detent torque part needs to be intentionally displaced from the coil center, so that the detent torque part stops at a magnetic pole center or neutral position in order to avoid start-up error. With a coil having a small inner diameter, such displacement angle cannot be made large. Unless a certain displacement angle can be maintained, the number of effective conductors that contribute to torque and the position thereof are sacrificed, leading to reduction of starting torque.
In addition, there has been demand for a long life, extremely thin brushless vibration motor for use as silent call means in accordance with the recent trend of thinner portable devices. However, when thickness is to be less than 2 mm, rotor thickness and drive circuit member thickness are a problem, with the natural result being that the thickness of the rotor is sacrificed, making it difficult to secure adequate vibration.
Further, with a small brushless vibration motor, in order to shift the center of gravity of the rotor itself in the radial direction so as to generate centrifugal vibrations, a sintered tungsten alloy eccentric weight must be attached.
It is conceivable to use adhesion, spot welding by laser or other means for fixing such eccentric weight to a magnetic iron alloy rotor yoke. However, adhesion is not sufficient to achieve reliable impact resistance. Also, because tungsten has a higher melting point than a metal to be welded thereto, when welding by laser, it is difficult to weld tungsten to, for example, the above magnetic iron alloy.
Thus, an object of the present invention is to provide a very thin stator configured so that even when a drive circuit member is thicker than armature coils, the rotor is not sacrificed to accommodate the thickness of the drive circuit member, as well as an axial air-gap brushless vibration motor equipped with such stator.
A further object of the present invention is to provide a very thin stator configured so that the disposition thickness of detent torque parts of a detent torque generation member can be completely ignored, and regardless of coil inner diameter, a prescribed optimal detent torque generation member position (displacement angle) can be obtained, as well as an axial air-gap brushless vibration motor equipped with such stator.
A still further object of the present invention is to provide an eccentric rotor to be combined with the above very thin stator with strong attachment with the eccentric weight, as well as an axial air-gap brushless vibration motor equipped therewith.